1. Field of the Invention
The present invention relates to micro-scale and nano-scale devices. More particularly, the present invention relates to electrical insulation of micro-scale and nano-scale devices for use in aqueous environments.
2. Description of the Related Technology
Due to the small size of micro- and nano-devices, the insulation layer must be very thin, and yet effective for electrical insulation so as not to adversely affect the mechanical performance of the micro-/nano-devices. In addition, the method for providing the insulation layer on the devices must also be economical for large scale industrial applications.
In biosensing applications, the micro-/nano-devices must be electrically insulated in a manner that allows them to be completely submerged in aqueous ionic buffers without a short circuit. In addition, the insulation layer must be able to accommodate immobilization of a receptor on the insulation layer and exhibit good bonding with the electrode surface, as well as with the immobilized receptor.
Thin ceramic layers such as MgO (C. Bondoux, P. Prené, P. Belleville, F. Guillet, S. Lambert, B. Minot and R. Jérisian, “MgO Insulating Films Prepared by Sol-gel Route for SiC Substrate,” J Europ. Ceram, Soc., 25(12), 2795-2798 (2005)); as well as Al2O3, Si3N4, Ta2O5, TiO2, BaTiO3 and SrTiO3 (P. Katiyar, C. Jin and R. J. Narayan, “Electrical Properties of Amorphous Aluminum Oxide Thin Films,” Acta Materialia, 53(9), 2617-2622, (2005) and the references cited therein) (Nguyen, L. T. T. et al., cited infra) have been shown to be effective insulation layers, but they require high-vacuum chemical vapor deposition (CVD) for applications. CVD is expensive and slow. Although polymeric insulation coatings such as polyimides (L. T. T. Nguyen, H. N. Nguyen and T. H. T. La, “Synthesis and Characterization of a Photosensitive Polyimide Precursor and its Photocuring Behavior for Lithography Applications,” Optical Materials, In Press, Corrected Proof, Available online 3 Jan. 2006, (http://www.sciencedirect.com/science/article/B6TXP-4HYD9 KB-3/2/bb4da50c417e914af8950e8ba0ceb1b3 and S. H. Cho, S. H. Kim, N.-E. Lee, H. M. Kim and Y. W. Nam, “Micro-Scale Metallization on Flexible Polyimide Substrate by Cu Electroplating Using SU-8 Photoresist Mask,” Thin Solid Films, 475, 1-2, Proceedings of the 4th Asian-European International Conference on Plasma Surface Engineering, 22 Mar. 2005, Pages 68-71. (http://www.sciencedirect.com/science/article/B6TW0-4DTKFCN 5/2/100c045e03c50e9a3aee6120537ded2a), and benzocyclobutene (BCB) (M. Ohnmacht, V. Seidemann and S. Buttgenbach, “Microcoils and Microrelays: an Optimized Multilayer Fabrication Process,” Sensors and Actuators, 83, 124-129 (2000)), can be deposited using a wet solution method, they require a thickness of tens of microns to be effective, too thick for micro-/nano-device applications. Thinner polymeric layers, such as parylene, require use of CVD for applications (D. Feili, M. Schuettler, T. Doerge, S. Kammer, and T. Stieglitz, “Encapsulation of Organic Field Effect Transistors for Flexible Biomedical Microimplants,” Sensors and Actuators, A, 120, 101-109 (2005) and K. S. Hwang, J. H. Lee, J. Park, D. S. Yoon, J. H. Park and T. S. Kim, “In-situ Quantitative Analysis of a Prostate-Specific Antigen (PSA) Using a Nanomechanical PZT Cantilever,” Lab Chip 4, 547 (2004)). Additional disadvantages of parylene include poor adhesion to the electrode surface (A. Khabari and F. K. Urban III, “Partially Ionized Beam Deposition of Parylene,” J. Non-Crystalline Solids, 351, 3536-3541 (2005)) and difficulties in the subsequent step of receptor immobilization (Feili, D. et al., cited infra).
In summary, the disadvantages of the current insulation methods include:                (1) Requiring high-vacuum physical or chemical vapor deposition, which is expensive and slow,        (2) Requiring a thicker layer than the thickness of the insulation layers achieved by the present invention,        (3) Lacking the ability to covalently bond to the electrode surface, and/or        (4) Lacking the ability to covalently bond to provide an immobilized antibody/receptor.Recently, a patent application was for a piezoelectric biosensor which can perform rapid, direct, and in situ detection of various molecular species in liquid (W. Y. Shih, W.-H. Shih, and Z. Shen, “Piezoelectric Cantilever Sensor,” Patent Application No. PCT/US2004/036705, Oct. 27, 2004).        
Accordingly, there is a need in the art for improved insulation layers for use in electromechanical devices.